There are great numbers of industrial processes requiring that manufactured parts be cleaned by application of chemical solvents either by immersing in a solvent bath or by spraying the parts with a solvent. After a period of time the solvent due to repetitive use becomes spent in that it is contaminated with debris, absorbed chemicals and other solvent deterioriating agents. For example, in the manufacture of printed circuit boards, electrical components are mounted on the boards with terminal leads extending through the board into proximity with circuit patterns formed on the underside of the board. In order to obtain electrical connections between the terminals and the circuit paths, the boards are subject to mass soldering operations. In mass soldering the usual practice is to move the board to advance the terminals through a flux applying station whereafter the boards are moved to advance the terminals through a solder wave. Following the soldering operation, it is necessary that the boards be cleaned with a solvent to remove the residual flux because the flux often contains conductive materials that may bridge conductive paths resulting in shorted circuits.
This solvent cleaning operation involves either immersion of the board in a solvent or the spraying of the soldered terminals with a solvent. In either case, the solvent becomes contaminated with dissolved flux and other debris picked up from the circuit boards. The solvent is relatively expensive and, hence, it is common practice to distill the solvent in order to recover as much of the solvent as possible by separating out the residue dissolved flux and other impurities. The usual salvage, distillation process results in reclaiming a substantial portion of the solvent, but a significant amount of residue slurry is produced which is a mixture of unvaporized solvent, flux, other chemicals, debris of various types, such as dirt, solder slivers, circuit board particles, etc. This residue presents a problem in that it must be economically disposed of without any adverse environmental effects. In view of the mass and chemical composition of the residue, which is in the form of a slurry, the safe disposal results in a rather expensive operation.
There are numerous distillation systems for separating contaminants from a solution. Many of these processes contemplate introducing a distilland onto a vaporized surface, such as a heated plate mounted in a distillation chamber which may be rotated to centrifugally distribute the distilland while it is vaporized. In other installations a scraper may pass over a stationary heated plate to spread the distilland and, hence, speed up the vaporization process. The vapors are usually condensed on a cooling surface provided in or by the upper portion of the distillation chamber. The condensed vapors or distillate run down the sides of the chamber into peripheral collecting troughs and then out of the chamber into a suitable container.
In U.S. Pat. No. 3,347,754 to W. L. Thomas issued Oct. 17, 1967, there is shown a high vacuum distillation system wherein the distilland is deposited at the center of a rotating plate which functions to centrifugally distribute the distilland relative to a number of condensing zones. The distilland is vaporized and condensed a number of times as it moves to the periphery of the rotating plate. The unvaporized residue passes through ducts formed in the plate and is collected and fed into a residue receiver.
In another system, such as shown in U.S. Pat. No. 2,818,373 to C. Ockrent issued Dec. 23, 1957, the distilland is fed onto a stationary heated plate whereafter a scraper spreads the distilland during vaporization. Again the vapors are condensed in the upper portion of the distillation chamber and collected in an inner circumferential trough and then exited from the chamber into a suitable container.